This invention relates to an electric motor-driven type fluid pump, and particularly to an electric motor-driven fuel pump for forcedly feeding fuel from a fuel tank to an engine in an internal combustion engine for vehicle.
FIG. 5 is a vertical sectional view showing a conventional electric motor-driven fuel pump disclosed in, for example, JP-B-7-3239, and FIG. 6 is an enlarged sectional view taken along line VIxe2x80x94VI of FIG. 5, and FIG. 7 is an illustration of a radial load distribution occurring in a pump flow path, and FIG. 8 is an illustration of bearing repulsion forces with respect to a load applied to an impeller.
In the drawings, numeral 1 shows an assembly of a pump casing, and this pump casing assembly 1 comprises a pump casing body 2 and a cover 3, and a disk-shaped impeller 4 having blades 5 along the outer circumferential edge is held in the pump casing assembly 1, and this impeller 4 is rotatably supported by a center shaft 6 described below.
The pump casing assembly 1 holds a pump flow path 7 with a circular arc band shape extending along the blades 5 of the impeller 4, and a suction port 8 and a discharge port 9 are opened in both ends of the pump flow path 7. Also, a center shaft 6 of a rotor 16 of an electric motor 15 is fitted in the center of the impeller 4, and both ends of the rotor 16 are rotatably supported by a bearing 17 and a bearing 18 provided in each of the pump casing assembly 1 and a bracket 24.
The pump casing assembly 1 and an end cover 19 are mutually connected by a cylindrical yoke 20 of the electric motor 15, and a permanent magnet 25 is annularly provided in an inner circumference of the yoke 20, and the rotor 16 is held inside this permanent magnet 25. Also, a liquid chamber 21 for storing fuel discharged from the discharge port 9 is provided between the pump casing assembly 1 and the end cover 19, and this liquid chamber 21 is in communicative connection with a liquid outlet 23 having a check valve 22 provided in the end cover 19, and the bracket 24 is provided with a brush 27 for feeding for sliding to a commutator 26 for supplying a current to a winding (not shown) of the rotor 16.
Next, operations of the conventional electric motor-driven fuel pump will be described.
In the electric motor-driven fuel pump constructed as described above, by rotating and driving (FIG. 6) the impeller 4 in a clockwise direction by the electric motor 15, fuel is sucked from the suction port 8 to one end of the pump flow path 7, and this fuel is increased in pressure while flowing through the pump flow path 7 in a clockwise direction and passes the liquid chamber 21 from the discharge port 9 of the other end and is discharged from the liquid outlet 23 through the check valve 22.
Incidentally, at the time of the increase in pressure, in the outer circumferential edge of the impeller 4, a radial load distribution 10 (FIG. 7) by a pressure distribution increasing from the suction port 8 toward the discharge port 9 occurs within the pump flow path 7 and as the resultant force, a radial load 11 (hereinafter called xe2x80x9cimpeller load 11xe2x80x9d) acts on the impeller 4. As a result of that, while the impeller load 11 is applied to the center shaft 6 of the rotor 16 fitted in the impeller 4, bearing repulsion forces 12, 13 (FIG. 8) act on the center shaft 6 from the bearing 17 and the bearing 18 rotatably supporting the center shaft 6. At the same time, a bearing load with the same size as that of the bearing repulsion forces 12, 13 in the opposite direction of the bearing repulsion forces 12, 13 acts on the bearing 17 and the bearing 18.
For use as a fuel pump of an internal combustion engine for vehicle, for example, in the pump in which a discharge pressure at the time of discharging fuel from the liquid outlet 23 is 250 kPa, the impeller load 11 reaches as large as about 1 kgf, and a discharge pressure of the fuel pump tends to be increasing year after year for the purpose of improvements in efficiency of the internal combustion engine for vehicle for supplying the fuel and exhaust gas, etc. and the impeller load is also increasing accordingly.
Since the conventional electric motor-driven fuel pump is constructed as described above, when a load applied to the bearings 17, 18 by the impeller load 11 increases, power consumption of the electric motor 15 increases due to an increase in a sliding resistance between the center shaft 6 and the bearings 17, 18, and efficiency of the electric motor-driven fuel pump is reduced. Also, there was a problem that wear in a contact portion with the center shaft 6 of the bearings 17, 18 increases.
This invention is implemented to solve such problems, and an object of the invention is to obtain an electric motor-driven fuel pump wherein the efficiency of the fuel pump is increased and wear in bearings is decreased by reducing a bearing load by an impeller load.
With an electric motor-driven fuel pump according to this invention, in the electric motor-driven fuel pump comprising a disk-shaped impeller having blades in the outer circumferential edge, a pump casing assembly which rotatably supports the impeller and provides a pump flow path with a circular arc band shape extending along the blades of the impeller and a suction port and a discharge port opened in both ends of said pump flow path, a rotor having a center shaft fitted in the center of the impeller and a core fixed in said center shaft, bearings for rotatably supporting the center shaft of the rotor, and a pair of permanent magnets concentrically provided in an outer circumference of the rotor, and the permanent magnets are placed so that a load of a direction opposite to a direction of a load applied to the impeller by a pressure distribution within the pump flow path is generated in the rotor.
Also, the permanent magnets are placed in both sides on the basis of a centerline of the rotor perpendicular to a direction of a load applied to the impeller, and also as viewed from the side generating the load, an axial center of the opposite permanent magnet is placed with the axial center offset to the side of the impeller from an axial center of the other permanent magnet.
Also, an offset distance between an axial center of one permanent magnet and an axial center of the core is equal to an offset distance between an axial center of the other permanent magnet and the axial center of the core, and offset directions are mutually the opposite directions.
Also, the permanent magnet close to the impeller is positioned by an adjusting protrusion.